Mechanical resonator for normal frequency oscillators in time-keepers



Aug. 30, 1966 H. WALDBURGER 3,269,106

MECHANICAL RESONATOR FOR NORMAL FREQUENCY OSCILLATORS IN TIME-KEEPERS Filed Jan. 11, 1965 MM gfzg 10%; W

United States Patent 3,269,106 MECHANICAL RESONATOR FOR NORMAL FRE- QUENCY OSCILLATORS IN TIME-KEEiERS Heinz Waldburger, Neuehatel, Switzerland, assignor to Centre Electronique Horloger S.A., Neuchatel, Switzerland, a corporation of Switzerland Filed Jan. 11, 1965, Ser. No. 424,751 Claims priority, applicatisor/s6witzerland, Jan. 20, 1964, 8 4

10 Claims. (Cl. 58-23) The use of magnetically or electrically driven and electronically controlled elastic resonators as time standards has been known for some time. The interest in such oscillators, however, has considerably increased, since a tuning fork with weighted branches has been used as a remarkably precise time standard in a wrist watch.

H-shaped and O-shaped resonators of various designs have also become known, which can be used for fitting in wrist watches and the like, whilst the following four main characteristics, amongst others, must be required of them; small position error, high quality factor, high isochronism and low frequency.

The influence on the frequency of an elastically mounted mass point of a modification of its position in a gravitational field depends mainly on the deviation of the trajectory of the mass point from a straight line. In the case of the weighted tuning fork the position error arising from this is relatively important compared to the other errors.

The position error can be compensated by the use of two tuning forks arranged in opposition (H-shaped resonator). This, however, has the disadvantage that an increase in frequency occurs for the same length and that there are four masses (and consequently difficulties in coupling).

The position error vanishes completely in the case of a known O-shaped flexion vibrator because the two vibrating rod members which are weighted in the middle, owing to their symmetry guide the motion of the two mass points along a common straight line. In this case the two spring members are connected to the securing points by elastic connecting pieces either arranged at each of their two ends or between them. This elastic connection of the resonance bodies proper (the dynamic effect of which corresponds to that of two vibrating rods which are weighted in the middle) is necessary in order to reduce the influence of the securing means on the frequency to an acceptable value. If the two flexion rods were to be secured directly at both ends, then the frequency would be dependent on the amplitude (isochronism error), owing to the fact that bending of the rods produces a non-linear increase of the normal forces. The influence of the securing means on the frequency is practically eliminated by the above-mentioned elastic suspension only for small amplitudes, and in addition, the quality factor is adversely influenced, owing to the fact that the securing points transmit small reaction forces (which compensate one another) to the rigid base plate, and that the spring members, which connect the resonator proper with the securing points, although necessary, do not take direct part with their bending elasticity in the resonance phenomenon and thus actually act as parasitic elements owing to their inner and outer friction.

This known mechanical resonator for normal frequency oscillators in time-keepers has two axes of symmetry which are at right angles to one another and of which the one forms the resonance straight line, and in addition, two masses oscillating in opposition on the resonance line as well as securing means, the securing point or rigidly connected securing points of which stand mathematically still in space. The present invention also con- "ice cerns a resonator of this known kind, which, however, does not offer the disadvantages mentioned above.

The resonator according to the invention is characterized by two identical swinging frames which are arranged symmetrically in relation to the axes of symmetry in such a manner that their longitudinal sides are halved by the resonance straight line, and which carry on each of their farther longitudinal sides an oscillating mass arranged symmetrically in relation to the resonance straight line, the securing means being arranged on the resonance straight line or symmetrically on either side of the same on the axis of symmetry and elastically connecting one to the other the two opposite longitudinal sides of the two swinging frames.

The resonator according to the invention makes it possible to prevent undesirable reactions at the securing points from influencing the frequency and the quality factor at any amplitude. In addition the resonator according to the invention can be designed in such a manner that, apart from the direct securing point, it comprises no partwhich does not contribute directly with its elasticity to the resonance phenomenon and the sole purpose of which would be to connect the oscillating parts elastically with the securing point. The securing points may easily be designed in such a manner that the frequency of the resonant oscillation of same direction may be reduced in a sufliciently pronounced degree in comparison with the resonant oscillation of opposite direction used for time measurement. Finally the reso na-tor according to the invention offers, compared to the O-shaped oscillator of known type mentioned above, the additional advantage that for the same construction length it oscillates at a lower frequency.

Four embodiments of the resonator according to the invention will now be described by way of examples with reference to the accompanying drawing.

FIGURE 1 shows a first, FIGURE 2 a second, FIG- URE 3 a third and FIGURE 4 a fourth embodiment seen from above in plan view.

In the first embodiment illustrated in FIGURE 1, two masses 1 are each symmetrically connected with the two spring frames 2 which determine the resonance, and which each consist of two parts, which are symmetrical in relation to the resonance straight line r and to the axes s* which are parallel to the axis of symmetry s which is at right angles to r. The two frames 2 are connected to one another by means of the two identical coupling members 3, and these in their turn are connected to the securing point 5 by means of the two identical members 4. The constructive design of the parts 3 and 4, which together form a T-shaped connecting piece, together with the other dimensions, determine the coupling between the two oscillating frames 2 as well as the (lower) frequency of the oscillation of same direction, which may naturally not be used owing to its reaction on the securing point, but which owing to its relation with the possible influence of disturbances has a certain importance. The cross section of the frame 2 is the same over the whole of its length, and it is to be noted that the elastic length of the frame has been reduced by a same amount in relation to the total length of the resonator by the masses and by the securing means.

The embodiment according to FIGURE 2 differs from the preceding one in four points. First of all the securing is effected in two securing points 15 symmetrically arranged in relation to the resonance straight line r, the two frames 12 being coupled by the members 13 and these being elastically connected to the securing points 15 by means of the cross-shaped member 14. Secondly, the four short sides 12a of the frames 12 are bent into loops in order to lessen the stiffness of the frame. Thirdly, the masses 11 are H-shaped, but also symmetrically arranged about the frame. Fourthly, the masses 11 are here secured to the frame and are made of another material as that of the latter.

In the case of the third embodiment illustrated in FIG- URE 3, the securing is effected in two symmetrical points 25 located on the axis of symmetry s, the two frames 22 being coupled by the member 23 and the latter being connected to the securing points 25 by the two members 24. The members 23 and 24 together form a cross-shaped holder. The frames 22 are made less stiff by a reduction in cross-section in the four edge parts 22a. The elastic length of the frame 22 is less reduced on the side corresponding to the securing points than on the side of the masses 21. These are only secured on one side to the frame 22.

FIGURE 4 illustrates a further securing possibility and a possible variant of the shape of the frame 32. The securing means make use of two securing points 35 symmetrically arranged on the axis 1', from which two identical members 34 lead to the two identical coupling members 33. The members 33 and 34 form a T-shaped elastic member. The masses 31 are identical with the masses 11.

In the illustrated embodiments the oscillating frames are of a generally elongated rectangular shape. These oscillating frames could be of any other given shape, provided of course that the symmetry in relation to the two axes of symmetry is preserved. For instance the oscillating frames could be made elliptical in shape. Finally it would also be possible to vary the cross-section of the frames, provided the necessary symmetry is observed.

What I claim is:

1. A mechanical resonator for normal frequency oscillators in time-keepers, with two axes of symmetry which are at right angles to one another and of which the one forms the resonance straight line, comprising two masses oscillating in opposition on the resonance line, securing means which stand mathematically still in space with relation to said masses, two substantially identical swinging frames having two opposite longitudinal and two opposite short sides arranged symmetrically in relation to the axes of symmetry in such a manner that the longitudinal sides are halved by the resonance straight line, said frames carrying on each of their farther longitudinal sides one of said oscillating masses arranged symmetrically in relation to the resonance straight line, said securing means being arranged symmetrically between said frames and elastically connecting the two adjacent longitudinal sides of said frames.

2. A resonator according to claim 1, wherein said frames comprise rods of constant cross-section.

3. A resonator according to claim 1 wherein said frames are substantially rectangular in shape.

4. A resonator according to claim 1, where said frames and said masses are made of different materials.

5. A resonator according to claim 1, wherein the short sides of said frames comprise at least one spring loop.

6. A resonator according to claim 1, wherein the short sides of said frames have a reduced cross-section.

7. A resonator according to claim 1, wherein two securing points are provided which lie symmetrically in relation to the centre on the resonance straight line, a crossshaped connection connecting said frames and said securing points together.

8. A resonator according to claim 1, .wherein two securing points are provided on the axis of symmetry which is perpendicular in relation to the resonance straight line and the coupling of said two frames and the connection with said securing points being effected by means of an elastic cross-shaped support.

9. A resonator according to claim 1, wherein two securing points are provided on the axis of symmetry which is perpendicular in relation to the resonance straight line and the coupling of said two frames and the connection with said securing points being effected by means of two T-shaped elastic members.

10. A mechanical resonator for normal frequency oscillators in time-keepers, with two axes of symmetry which are at right angles to one another and of which one forms the resonance straight line, comprising two masses oscillating in opposition on the resonance straight line, two substantially identical swinging frames having each two opposite longitudinal sides and two opposite short sides arranged symmetrically in relation to the axes of symmetry so that their longitudinal sides are halved by said resonance straight line, said frames carrying on each of their farther longitudinal sides one of said oscillating masses arranged symmetrically in relation to the resonance straight line, and securing means comprising two elastic T-shaped connecting pieces connecting the two adjacent longitudinal sides of said swinging-frames, and a securing point disposed at substantially the crossing of said two symmetry axes and standing mathematically still in space.

References Cited by the Examiner UNITED STATES PATENTS 3,170,278 2/1965 Stutz 5823 RICHARD B. WILKINSON, Primary Examiner.

G. F. BAKER, Assistant Examiner. 

1. A MECHANICAL RESONATOR FORM NORMAL FREQUENCY OSCILLATORS IN TIME-KEEPERS, WITH TWO AXES OF SYMMETRY WHICH ARE AT RIGHT ANGLES TO ONE ANOTHER AND OF WHICH THE ONE FORMS THE RESONANCE STRAIGHT LINE, COMPRISING TWO MASSES OSCILLATING IN OPPOSITION ON THE RESONANCE LINE, SECURING MEANS WHICH STAND MATHEMATICALLY STILL IN SPACE WITH RELATION TO SAID MASSES, TWO SUBSTANTIALLY IDENTICAL SWINGING FRAMES HAVING TWO OPPOSITE LONGITUDINAL AND TWO OPPOSITE SHORT SIDES ARRANGED SYMMETRICALLY IN RELATION TO THE AXES OF SYMMETRY IN SUCH MANNER THAT THE LONGITUDINAL SIDES ARE HALVED BY THE RESONANCE STRAIGHT LINE, SAID FRAMES CARRYING ON EACH OF THEIR FARTHER LONGITUDINAL SIDES ONE OF SAID OSCILLATING MASSES ARRANGED SYMMETRICALLY IN RELATION TO RESONANCE STRAIGHT LINE, SAID SECURING MEANS BEING ARRANGED SYMMETRICALLY BETWEEN SAID FRAMES AND ELASTICALLY CONNECTING THE TWO ADJACENT LONGITUDINAL SIDES OF SAID FRAMES. 